between the cable(be it coiled, straight or any other fancy one), its connected to the plug via soldering lead. To pull it hard, the probability of the whole cable(with the plug still intact) being pull out from the amp input jack or effect pedal input jack is much higher then the plug itself, getting dislodged with the cable.
Dont believe? Heh, go get any instrument cable with soldered plug and try to pull it apart, by hand. You need brute force for the thing to be separated, much higher than the normal/accidental pulling of guitar cable. The solder joint can withstand much higher force being exerted on it. Weakest link is the thin strand of cable thats being soldered.